Potential measuring apparatus

ABSTRACT

A potential measuring apparatus has a detection electrode on which an electric charge is induced according to a potential of a detection object, and a modulator for altering the generated quantity of the electric charge. The detection electrode has at least one depressed portion on a surface opposite to the detection object.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a potential measuring apparatus fordetecting a potential of a detection object through a quantity ofelectric charge generated in a detection electrode. The presentinvention also relates to an image forming apparatus equipped with thispotential measuring apparatus.

2. Related Background Art

Japanese Patent Application Laid-Open No. 2000-180490 has proposed apotential measuring apparatus of a system that a distance between adetection object and a detection electrode is changed. This potentialmeasuring apparatus comprises a piezoelectric tuning fork, an insulatorand a detection electrode and has the construction of the so-calledcapacitor in which the insulator is formed between the detectionelectrode and the piezoelectric tuning fork. In this construction,electric charge is generated, increased and decreased at the detectionelectrode whose distance to the detection object is changed, and thisincrease and decrease of electric charge becomes an AC electric signalfrom the detection electrode.

U.S. Pat. No. 6,177,800 has proposed a potential measuring apparatus ofa system that an area of a detection electrode as seen from a detectionobject is changed. This potential measuring apparatus is produced by theMEMS technique (application of a semiconductor process technique). Insemiconductor processes, silicon is generally used as a substratematerial. When the detection electrode is formed on silicon, aninsulator is formed between the silicon and the detection electrode.Since silicon has a nature that electricity is passed through it, theso-called capacitor is constructed. In this construction, electriccharge is generated, increased and decreased in the detection electrode,of which the area seen from the detection object is changed, and thisincrease and decrease of electric charge becomes an AC electric signalfrom the detection electrode.

The principle of generating an output signal in a potential measuringapparatus of a non-contact system, which is a system used in thepotential measuring apparatus of the prior art and the potentialmeasuring apparatus according to the present invention, will hereinafterbe described.

When a distance (g) between the detection object and the detectionelectrode a dielectric constant (ε) between the detection object and thedetection electrode, organ area (s) of the detection electrode as seenfrom the detection object is changed, an electric (coupling) capacitance(C) induced between the detection object and the detection electrode isaltered.

The electric capacitance (C) may be generally represented by thefollowing equation (1):C=(ε·s)/g  (1)wherein ε[F·m⁻¹] is a dielectric-constant between the detection objectand the detection electrode, g [m] is a distance between the detectionobject and the detection electrode, and s [m²] is an area of thedetection electrode as seen from the detection object.

The electric capacitance (C) may also be represented by the followingequation (2):Q=C×Vd  (2)wherein Q is a quantity of electric charge, and Vd [V] is a potential ofthe detection object.

The equation (1) is substituted into the equation (2) to obtain thefollowing equation (3):Q=(ε·s)/g×Vd  (−3)

When the area of the detection electrode as seen from the detectionobject is changed with time (t), the equation (3) can be represented bythe following equation (4). This change can be attained by, for example,letting in and out a shield plate formed of a conductive material or thelike between the detection object and the detection electrode.Q(t)=(ε·s(t))/g×Vd  (4)

The equation (4) is differentiated with respect to the time (t) toobtain the following equation (5):dQ(t)/dt=I(t)=(ε/g·ds(t)/dt)×Vd  (5)wherein the area change per time, ds(t)/dt, is a known value.

In this way, a current signal I(t) from the detection electrode isobtained in accordance with the equation (5). This signal is subjectedto current-voltage conversion, whereby a voltage output signal V(t) canbe obtained, and the potential Vd of the detection object can be foundfrom the output signal V(t). When the distance (g) between the detectionobject and the detection electrode is changed with time (t), or adielectric constant (ε) between the detection object and the detectionelectrode is changed with time (t), it is also understood that a currentsignal I(t) from the detection electrode is obtained in accordance withthe same way of thinking as described above.

However, in the potential measuring apparatus of the non-contact system,an electric capacitance (an electric capacitance exclusive of theelectric capacitance generated with respect to the detection object;hereinafter also referred to as a parasitic capacitance) is generatedbetween the detection electrode and a member present in the vicinitythereof. In some cases, a part of the electric signal generated at thedetection electrode may flow into the member present in the vicinity ofthe electrode by this parasitic capacitance. Therefore, there is apossibility that the output signal from the detection electrode may belowered. If a noise component is present in the member present in thevicinity of the detection electrode, the noise component flows into thedetection electrode, so that the signal-to-noise ratio (S/N ratio) maybe lowered in some cases. In the above-described prior art, this has notbeen taken into consideration.

SUMMARY OF THE INVENTION

There is provided a potential measuring apparatus comprising a detectionelectrode on which an electric charge is induced according to apotential of a detection object, and a altering means (or driving means)as a modulator for altering the generated quantity of the electriccharges wherein the detection electrode has depressed and projectedportions on a surface thereof opposite to the detection object, and theelectrode is not present at the depressed portions.

A present invention is directed to a potential measuring apparatuscomprising:

a detector having a detection electrode on which an electric charge isinduced according to a potential of an object, said detection electrodebeing disposed on an insulating surface of a support member; and

a modulator for altering a quantity of the electric charge which isinduced on said detection electrode;

wherein said detector has depressed and projected portions on a surfacethereof opposite to the object, and said detection electrode is notpresent at the depressed portions.

In this apparatus, the depressed portion includes, for example, at leastone through hole or groove or both of them. According to such aconstruction, an electric charge can be effectively generated at an edgeportion or a side wall formed by the depressed portion, or the holeand/or groove by electric lines of force from the detection object.

More specifically, the depressed portions, or the holes or grooves areprovided as illustrated in FIGS. 1A and 1B, whereby edge portions andside walls are produced in the detection electrode, and on the otherhand the area of the detection electrode opposite to a member forsupporting the detection electrode is decreased. The area of thedetection electrode as seen from the detection object is decreased, butthe edge portions and side walls exist, so that electric lines of forcealso concentrate on the edge portions and side walls when a potential isgenerated between the detection object and the detection electrode. As aresult, a difference in output signal between the presence of thedepressed portions or the holes or grooves and the absence thereof canbe eliminated almost completely or to some extent. On the other hand,since the area of the detection electrode opposite to the member forsupporting the detection electrode is decreased, a parasitic capacitancegenerated between them can be lowered.

According to the present invention, there is also provided an imageforming apparatus comprising the potential measuring apparatus describedabove and an image forming means, wherein the formation of an image bythe image forming means is controlled by means of an output signalobtained from the potential measuring apparatus. This image formingapparatus carries the potential measuring apparatus according to thepresent invention, so that an output signal having a relatively high S/Nratio can be obtained to grasp an exact potential of a detection object,whereby a charging treatment and a developing treatment to the detectionobject can be appropriately performed.

According to the present invention, there is also provided a potentialmeasuring apparatus comprising:

a detection electrode on which an electric charge is induced accordingto a potential of an object, said detection electrode being disposed onan insulating surface of a support member;

a modulator for altering a quantity of the electric charge which isinduced on said detection electrode;

wherein said detection electrode has a plurality of conductive portionsdisposed in isolation.

According to the present invention, there is also provided a potentialmeasuring apparatus comprising:

a detection electrode on which an electric charge is induced accordingto a potential of an object, said detection electrode being disposed onan insulating surface of a support member;

a modulator for altering a quantity of the electric charge which isinduced on said detection electrode; wherein said detection electrodehas a conductive pattern so that discrete portions of the insulatingsurface are exposed and disposed in isolation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates the constitution of a detector of a conventionalpotential measuring apparatus;

FIG. 1B illustrates the construction of a detector according to anembodiment of a potential measuring apparatus of the present inventionin comparison with a conventional one shown in FIG. 1A;

FIGS. 2A and 2B are cross-sectional views illustrating the relationshipbetween the construction of the detection electrode and the distributionof electric lines of force shown in FIGS. 1A and 1B respectively;

FIGS. 3A and 3B are cross-sectional views illustrating an example of anoperation for generating an output signal from the detection electrode;

FIGS. 4A, 4B, 4C and 4D are cross-sectional views illustrating anotherexample of an operation for generating an output signal from thedetection electrode;

FIGS. 5A, 5B, 5C and 5D illustrate a further example of an operation forgenerating an output signal from the detection electrode;

FIGS. 6A, 6B, 6C and 6D are plan views illustrating the constructions ofdetection electrodes according to other embodiments in the potentialmeasuring apparatus of the present invention;

FIG. 7 is a cross-sectional view illustrating the sectional constructionof a detection electrode according to a further embodiment in thepotential measuring apparatus of the present invention; and

FIG. 8 illustrates the construction of an exemplary image formingapparatus, in which the potential measuring apparatus according to thepresent invention is installed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will hereinafter be described with reference tothe drawings.

FIG. 1B illustrates the construction in the vicinity of a detectionelectrode according to a first embodiment of a potential measuringapparatus of the present invention in comparison with an ordinarydetection electrode of a potential measuring apparatus shown in FIG. 1A.FIG. 1A illustrates a section and a top face of the ordinary one beforeholes or grooves are formed in the detector. The detector comprises adetection electrode 101, an insulating layer 102 and a support member103. FIG. 1B illustrates a section (a section in a face perpendicular toa support member 103) and a top face (a face where a detection electrode110 is viewed from right above in a vertical direction) of a detectionelectrode 110 according to this embodiment, which is obtained by forminga plurality of through holes 104 in a flat plate-like detectionelectrode 101. The holes 104 almost perpendicular to the flat plate-likedetection electrode 101 are formed, thereby effectively forming edgeportions 105 having a substantially right angle and side walls 106substantially vertically extending. The holes 104 completely passingthrough the electrode 110 are formed, whereby an area of the detectionelectrode 110 opposite to the support member 103 through the insulatinglayer 102 is decreased. The area of the detection electrode 110 oppositeto the support member 103 is decreased, whereby a parasitic capacitancegenerated between them is lowered compared with the construction shownin FIG. 1A.

FIG. 2A is a cross-sectional view illustrating an arrangement relationbetween the detection electrode 101 before holes are formed and adetection object 201. FIG. 2B is a cross-sectional view illustrating anarrangement relation between the detection electrode 110 after holes 104are formed and the detection object 201. When the detection object 201is arranged so as to oppose to the detection electrode and a potentialdifference is created between the detection object 201 and the detectionelectrode 101 or 110, electric force lines 202 are generated. In thecase of FIG. 2B, the area of the detection electrode 110 as seen fromthe detection object 201 is small compared with the case of FIG. 2A.However, almost the same output signal as in the case of FIG. 2A can beobtained because the electric force lines 202 concentrate on the edgeportions 105, or reach the side walls 106. Even in this embodiment, aprocess for processing the output signal from the detection electrode110 in a signal processing circuit on the basis of the principledescribed above to detect a potential of the detection object 201 is thesame as the conventional process.

An example of the operation of the potential measuring apparatusaccording to this embodiment is described with reference to FIGS. 3A and3B.

The potential measuring apparatus according to the present inventionincludes an altering means (also refereed to as a modulator) forarranging the detection object and the detection electrode so as tooppose to each other and for altering the generated quantity of theelectric charge which is induced on the detection electrode.

The altering means (or the modulator) as used in the present inventionis not particularly limited so far as it alters the generated quantityof the electric charge which is induced on the detection electrode.Typical examples of the altering means (or the modulator) include onewhich alters the generated quantity of the electric charge by alteringthe distance between the detection object and the detection electrode aswell as one which alters the generated quantity of the electric chargeby altering the amount of electric lines of force that reach, thedetection electrode from the detection object using a shutter or thelike put between the detection object and the detection electrode.

In the case where the distance between the detection electrode 110 andthe detection object 201 is changed, thereby obtaining an output signalaccording to the potential of the detection object, for example, thedetection electrode 110 is moved upward and downward in a directionsubstantially perpendicular to a face of the detection electrode 110 asillustrated in FIGS. 3A and 3B. To achieve such movement, for example, adriving means or altering means is used in which a beam is formed at thesupport member 103, piezoelectric elements are formed on the beam or thesupport member, and voltage is applied to the piezoelectric elements toutilize their changes of shape. The detection electrode may also bemoved by forming a fixed-electrode on a part of the beam or supportmember so as to face a neighboring electrode for generatingelectrostatic attraction force and applying voltage between theelectrodes to generate electrostatic attraction force. Further, thedetection electrode may be moved by a driving means in which a coil (ormagnet) is formed on the beam, support member or the like, a magnet (orcoil) is formed in the vicinity thereof, and a current is allowed toflow through the coil to generate magnetic force, thereby producingrepulsion force or attraction force between the coil and the magnet.

The present invention is not limited to the driving means describedabove, and a motor vibration heat or the like may also be used.

The distance between the detection electrode 110 and the detectionobject 201 may also be changed as illustrated in FIGS. 4A to 4D. In thiscase, the detection electrode 110 is inclined as illustrated in FIGS. 4Ato 4D, thereby changing not only the distance, but also an area of thedetection electrode 110 as seen from the detection object 201. An outputsignal can be thereby more enlarged. The same driving method as in thedriving means illustrated in FIGS. 3A and 3B can be used for achievingsuch movement.

In this case, supposing that the inclined angle of the detectionelectrode 110 is θ, the width of each of the holes or grooves 104 is G,and the thickness of the detection electrode 110 is H as illustrated inFIGS. 4B and 4C, the bottoms of the holes or grooves 104 become in astate of not being seen from, the detection object 201 as illustrated inFIG. 4D so far as the following equation (6) is satisfied. In otherwords, almost all electric lines of force coming from the detectionobject 201 to the area within the outermost contour of the detectionelectrode 110 become in a state of being received by the detectionelectrode 110 like the case where the holes or grooves 104 are notformed. As a result, an output signal equivalent to the output signalobtained by using the detection electrode 101, in which the holes orgrooves 104 are not formed can be obtained.tan θ≧G/H  (6)

In this case, the area of the detection electrode 110 opposed to thesupport member 103 through the insulating layer 102 can be made smalleras the width W of the detection electrode 110 is smaller, so that aparasitic capacitance can be made small. It goes without saying that theelectric lines of force concentrate on the edge portions 105 of thedetection electrode 110 as described in the case of FIG. 2B even whenthe inclined angle of the detection electrode 110 is smaller than theabove θ. The electric lines of force further reach the side walls 106.Accordingly, an output signal close to the output signal obtained byusing the detection electrode 101, in which the holes or grooves 104 arenot formed, can be obtained.

An output signal may also be obtained by changing a dielectric constantbetween the detection object 201 and the detection electrode 110 asillustrated in FIGS. 5A to 5D. This also means that the area of thedetection electrode 110 as seen from the detection object 201 is changedby inserting a shield plate between the detection object 201 and thedetection electrode 110. When the output signal is obtained by changingthe dielectric constant (ε) or the area (s) in the above-describedmanner, a material (dielectric 501) having a dielectric constantdifferent from that of the surroundings is let in and out between thedetection object and the detection electrode. Alternatively, a conductoris let in and out. The same method as that by the driving meansillustrated in FIGS. 3A and 3B may be used for the purpose of lettingthe dielectric or conductor in and out. In order to change thedielectric constant between the detection object 201 and the detectionelectrode 110, for example, the dielectric constant of the materialprovided between the detection object 201 and the detection electrode110 may also be changed by electrical control in addition to theabove-described method.

When a plurality of the constructions illustrated in FIG. 5B arearranged (in a state that a plurality of the detection electrodes 110are electrically connected to each other), an output signal as large asthe arranged number of the detection electrodes can be obtained. When aconstruction in which the dielectrics 501 or the conductors 502 arepartially connected to each other is used a plurality of the dielectrics501 or the conductors 502 may also be moved at once by one source ofdriving. FIG. 5C illustrates a section taken along a plane perpendicularto the support member 103, and FIG. 5D illustrates a top face where aplurality of the detection electrodes 110 are viewed from right above ina vertical direction.

The methods for obtaining the above-described various output signals maybe used in various combinations. For example, the dielectric 501 or theconductor 502 may be let in and out between the detection object 201 andthe detection electrode 110 while vertically moving the detectionelectrode 110. An output signal greater in amplitude can be therebyobtained.

FIGS. 6A and 6B and 6C and 6D illustrating a top face where thedetection electrodes 110 is viewed from right above in a verticaldirection respectively illustrates the forms of detection electrodes 310and 410 and 610 and 710 according to further embodiments in thepotential measuring apparatus of the present invention. The form of eachhole 104 may be either polygonal or circular (elliptic). Some of theholes 104 may be opened out at a side of the detection electrode 310 asillustrated in FIG. 6A. Alternatively, the detection electrode may havesuch a construction that grooves 104 long in one direction and openedout at a side of the detection-electrode 410 are formed as illustratedin FIG. 6B. Furthermore, the detection electrode may also have such aconstruction that rectangular grooves are combined with a grooveextending in one direction as illustrated in FIGS. 6C and 6D.

The groove may be formed not only linearly but also curvilinearly.

The depressed portions formed in the detection electrode may be holes orgrooves some of which do not pass through, or may be formed not only ina regular pattern, but also in a somewhat random pattern. The patternviewed from above is not limited to a rectangular form, but may also bea curvilinear form. However, it is desirable that many edge portions arepresent at the holes or grooves because the electric lines of force arelikely to concentrate thereon.

FIG. 7 is a cross-sectional view illustrating the sectional construction(a sectional form taken along a plane perpendicular to the supportmember 103) of a detection electrode according to a still furtherembodiment of the potential measuring apparatus of the presentinvention. It is not necessary that the side wall of the hole or groove104 is perpendicular to the flat plate-like support member 103 as shownin the above-described embodiments. The sectional form may preferably beof a reverse tapered form as illustrated in FIG. 7. The reverse taperedform keeps large the area of the detection electrode 510 as seen fromthe detection object, while further reducing the area of the detectionelectrode 510 opposite to the support member 103. Accordingly, using thedetection electrode 510 having the reverse tapered form achieves a highS/N ratio. In this case, even when the sectional form (generallyreferred to as a forward tapered form) is a tapered form in which theinclination is reverse to that shown in FIG. 7, the effect of thepresent invention may be exhibited to a certain extent. Even when theedge portion 105 in FIG. 1B is not in an angular form, but is in a formincluding a curved surface, the effect of the present invention may alsobe exhibited to a certain extent.

Table 1 showing a relationship between the rate of the respectivedimensions of the detection electrode 110 illustrated in FIG. 4C and thepercentage reduction of output will hereinafter be described. TABLE 1Width W Height H Percentage of Width G of Percentage reduction ofdetection of hole detection reduction parasitic Type electrode or grooveelectrode of output capacitance (1) 1 2 5 About 2% About 67% (2) 2 4 5About 10% About 67% (3) 2 4 1 About 33% About 67% (4) 4 8 1 About 50%About 67%

ANSYS (electromagnetic field analyzing software; product of CybernetSystems Co., Ltd.) is used in determining the above relationship. Theintensity of the output signal obtained in the case where neither holesnor grooves are formed in the detection electrode is regarded as 100% toshow the percentage reduction of output signal in the case where grooves104 are formed. The groove pattern of the detection electrode 110 inthis embodiment is the so-called line-and-space pattern as illustratedin FIG. 6B.

First, since the ratio of the width G of the groove to the width W ofthe detection electrode is 2 in any type, it is understood that the areaof the detection electrode 110 opposite to the support member 103 can bereduced to about 67%. The parasitic capacitance can also be therebyreduced by almost the same percentage as in the area. Second, it isunderstood that the percentage reduction of output becomes low as theheight H of the detection electrode 110 increases. The percentagereduction % of output can be suppressed to about 2% in the dimensionalratio of, for example, the type (1).

It is understood from the above results that the parasitic capacitancecan be reduced to a relatively considerable extent with the outputsignal hardly reduced or not too much reduced by forming the depressedportions including either one or both of the through holes and groovesin the detection electrode. When the absolute value of the height H ofthe detection electrode can hot be increased so much (for example, whenthe detection electrode is formed by a film forming method such assputtering or vapor deposition), the construction of the type (1) can berelatively created by decreasing the width W of the detection electrodeand the width G or the holes or grooves. In this case, the number of theholes or grooves is increased when the size, form and the like of theoutermost contour of the detection electrode are fixed.

In Table 1, the ratio of the width W of the detection electrode to thewidth G of the holes or grooves is 1:2. When this ratio is, for example,1:a value-greater than 2, however, the percentage reduction of outputcomes to increase. In order to prevent this, it is only necessary toincrease the height H of the detection electrode.

FIG. 8 illustrates a typical construction of an exemplary image formingapparatus, in which the potential measuring apparatus according to thepresent invention is installed. This image forming apparatus comprises apotential measuring apparatus 801 according to the present invention, acharger 802, a signal processor 803, a high voltage generator 804, anexposer 805, a toner supply system 806, a transfer-printing medium feedroller 807, a photosensitive drum 808 as a photoreceptor and atransfer-printing medium 809.

The apparatus is operated in the following manner. (1) The drum 808 ischarged by the charger 802. (2) The charged portion is exposed with theexposer 805 to obtain a latent image. (3) A toner is applied to thelatent image by the toner supply system 806 to obtain a toner image. (4)The toner image is transferred to the transfer-printing medium 809. (5)The toner on the transfer-printing medium 809 is melted and fixed. Theformation of an image is achieved through these steps. At this time, thecharged state of the drum 808 is determined by the potential measuringapparatus 801, and the result thereof is processed by means of thesignal processor 803 and feedback is carried out onto the high voltagegenerator 804 as needed, whereby stable charging of the drum can berealized to realize stable formation of an image.

According to the above-described potential measuring apparatus of thepresent invention, a parasitic capacitance can be reduced with thequantity of an electric capacitance generated between the detectionobject and the detection electrode hardly reduced or not too muchreduced by virtue of such unique form of the detection electrode asdescribed above, and so the S/N ratio can be made relatively high. Theimage forming apparatus, in which the potential measuring apparatusaccording to the present invention is installed, permits forming animage of relatively high quality on the basis of relatively accurateinformation as to the potential of a detection object, which is obtainedby the potential measuring apparatus according to the present invention.

This application claims priority from Japanese Patent Application No.2005-156461 filed on May 27, 2005, which is hereby incorporated byreference herein

1. A potential measuring apparatus comprising: a detector having a detection electrode on which an electric charge it induced according to a potential of an object, said detection electrode being disposed on an insulating surface of a support member; and a modulator for altering a quantity of the electric charge which is induced on said detection electrode, wherein said detector has depressed and projected portions on a surface thereof opposite to the object, and said detection electrode is not present at the depressed portions.
 2. The potential measuring apparatus according to claim 1, wherein the depressed portion of the detector includes at least one of a through hole and a through groove.
 3. The potential measuring apparatus according to claim 1, wherein an area of an upper surface of the projected portion is lager than that of a lower surface of the projected portion.
 4. The potential measuring apparatus according to claim 1, wherein the modulator alters a distance between the object and the detection electrode.
 5. The potential measuring apparatus according to claim 1, wherein the modulator alters an inclination of the detection electrode to the object to change a distance between the object and the detection electrode or to change an area of the detection electrode as seen from the object.
 6. The potential measuring apparatus according to claim 1, wherein the modulator alters a dielectric constant between the object and the detection electrode.
 7. The potential measuring apparatus according to claim 1, wherein the modulator lets a shield member in and out between the object and the detection electrode to change an area of the detection electrode as seen from the object.
 8. An image forming apparatus comprising the potential measuring apparatus according to claim 1 and an image forming means comprising a photoreceptor as the object, wherein formation of an image by the image forming means is controlled by means of an output signal obtained from the potential measuring apparatus.
 9. A potential measuring apparatus comprising: a detection electrode on which an electric charge is induced according to a potential of an object, said detection electrode being disposed on an insulating surface of a support member; a modulator for altering a quantity of the electric charge which is induced on said detection electrode; wherein said detection electrode has a plurality of conductive portions disposed in isolation.
 10. A potential measuring apparatus comprising: a detection electrode on which an electric charge is induced according to a potential of an object, said detection electrode being disposed on an insulating surface of a support member; a modulator for altering a quantity of the electric charge which is induced on said detection electrode; wherein said detection electrode has a conductive pattern so that discrete portions of the insulating surface are exposed and disposed in isolation. 